PXEBOOT(8)

🌸 PXEBOOT(8) — the glow-up era of bootloaders 🌸

okay so bestie, let me tell you about pxeboot — it's the Preboot Execution Environment (PXE) bootloader, and honestly? it's giving main character energy in the diskless-machine world. 💅

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✨ NAME ✨

pxeboot — Preboot Execution Environment (PXE) bootloader. yeah. that's the whole name. iconic, brief, slay. 🎀

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🦋 DESCRIPTION 🦋

okay so first things first: the pxeboot bootloader is literally a modified version of the system third-stage bootstrap loader(8), but it's been configured to run under Intel's Preboot Execution Environment (PXE) system. PXE is basically a form of smart boot ROM — no cap — and it's built into Intel EtherExpress Pro/100 and 3Com 3c905c Ethernet cards, plus Ethernet-equipped Intel motherboards. PXE supports DHCP configuration AND provides low-level NIC access services. it's doing the most, and we love that for it. 🔥

the DHCP client will set a DHCP user class named FreeBSD to allow flexible configuration of the DHCP server. yes bestie, it's tagged. iykyk. 💜

the pxeboot bootloader retrieves the kernel, modules, and other files either via NFS over UDP or by TFTP, selectable through compile-time options. and when you combine it with a memory file system image or an NFS-mounted root file system, pxeboot allows for easy, EEPROM-burner free construction of diskless machines. literally no EEPROM burner required. we are thriving. ✨

the pxeboot binary is loaded just like any other boot file — you just specify it in the DHCP server's configuration file. below is a sample configuration for the ISC DHCP v3 server, and yes i'm pasting it exactly because details matter and i would never do you dirty like that:

option domain-name "example.com";
option routers 10.0.0.1;
option subnet-mask 255.255.255.0;
option broadcast-address 10.0.0.255;
option domain-name-servers 10.0.0.1;
server-name "DHCPserver";
server-identifier 10.0.0.1;
next-server 10.0.0.1;

default-lease-time 120;
max-lease-time 120;

subnet 10.0.0.0 netmask 255.255.255.0 {
       filename "pxeboot";
       range 10.0.0.10 10.0.0.254;
       if exists user-class and option user-class = "FreeBSD" {
            option root-path "tftp://10.0.0.1/FreeBSD";
       }
}

next-server is the IP address of the next server in the bootstrap process — i.e. your TFTP server or NFS server. pxeboot recognizes option root-path directives as the server and path to NFS mount for file requests, respectively, or the server to make TFTP requests to. and like, note this: pxeboot expects to fetch /boot/loader.rc from the specified server before loading any other files. so don't skip that step, bestie. 🙈

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🎀 valid option root-path syntax 🎀

here's the whole menu, and you already know i'm listing every single one:

• /path — path to the root filesystem on the NFS server
• ip://path — path to the root filesystem on the NFS server ip
• nfs://path — path to the root filesystem on the NFS server
• nfs://ip/path — path to the root filesystem on the NFS server ip
• tftp://path — path to the root filesystem on the TFTP server
• tftp://ip/path — path to the root filesystem on the TFTP server ip

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🌈 a lil note on packet sizes 🌈

pxeboot defaults to a conservative 1024 byte NFS data packet size — very demure, very mindful. this may be changed by setting the nfs.read_size variable in /boot/loader.conf. valid values range from 1024 to 16384 bytes. so like, don't go rogue and put 99. the range is the range. ⭐

in all other respects, pxeboot acts just like loader(8). periodt. 💅

for further information on Intel's PXE specifications and Wired for Management (WfM) systems, see http://www.pix.net/software/pxeboot/archive/pxespec.pdf. go read it, it's giving homework but make it networking. 📚

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🫶 SEE ALSO 🫶

• loader(8)

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💖 HISTORY 💖

the pxeboot bootloader first appeared in FreeBSD 4.1. a true pioneer. we stan an OG. 👑

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🧚 AUTHORS 🧚

the pxeboot bootloader was written by John Baldwin <jhb@FreeBSD.org> and Paul Saab <ps@FreeBSD.org>. this manual page was written by Doug White <dwhite@FreeBSD.org>. absolute legends, every single one. no cap. 🌟

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and that's the whole thing bestie — from Debian, dated February 15, 2021. you're welcome, go boot something diskless and think of me. 💜✨🦋